An investigation on the two-photon absorption activity of various terpyridines and related homoleptic and heteroleptic cationic Zn(II) complexes

Article abstract of DOI:10.1039/b515129e

The two-photon absorption (TPA) properties of various terpyridines of the kind [4′-(C₆H₄-p-X)-2,2′6′,2″- terpyridine] and related homoleptic and heteroleptic bis(terpyridine) cationic zinc(ii) complexes were investigated by the TPA i

Full text of DOI:10.1039/b515129e

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
An investigation on the two-photon absorption activity of various
terpyridines and related homoleptic and heteroleptic cationic Zn(II)
complexes
Stefania Righetto,a Sergio Rondena,a Danika Locatelli,a Dominique Roberto,*a Francesca Tessore,a
Renato Ugo,a Silvio Quici,b Silvia Roma,b Dmitry Korystovc and Vojislav I. Srdanovc
Received 25th October 2005, Accepted 22nd December 2005
First published as an Advance Article on the web 25th January 2006
DOI: 10.1039/b515129e
The two-photon absorption (TPA) properties of various terpyridines of the kind [49-(C6H4-p-X)-
2,29:69,20-terpyridine] and related homoleptic and heteroleptic bis(terpyridine) cationic zinc(II)
complexes were investigated by the TPA induced photoluminescence (TPA-PL) method in a
femtosecond regime. It appeared that terpyridines bearing an X donor group are characterized by
TPA cross sections among the largest ever reported for a molecule with a dipole symmetry
whereas coordination to a Zn(II) center leads to a decrease of the TPA response.
compounds with TPA properties which has been largely
1. Introduction
limited up to now to organic compounds, prompted us to
Molecular nonresonant two-photon absorption (TPA) has
investigate the TPA properties of other p-delocalized nitrogen
attracted growing interest over recent years due to the many
donor ligands such as terpyridines and related zinc(II)
applications it offers both in material science and in biological
imaging.1 For this reason, molecular engineering directed
complexes. In order to evaluate TPA cross section (d) values,
we used the TPA induced photoluminescence (TPA-PL)
method8 in a femtosecond regime. This helps reduce excited-
towards TPA optimization has become very active, leading to
a range of molecules of various symmetries including dipoles,2
state absorption events which can lead to artificially enhanced
quadrupoles,3 octupoles,4 and branched structures.5 Most
effective TPA cross-section values when nanosecond pulses
are used.1d,e
dipolar chromophores exhibit a smaller two-photon absorp-
tion cross-section in comparison with some quadrupolar and
octupolar derivatives. However, combining dipolar branches
2. Results and discussion
within a three-branched octupolar structure can induce a very
intense TPA response.1f Therefore there is a need for new
Various terpyridines bearing an electron donor or electron
withdrawing substituent
X of the kind [49-(C6H4-p-X)-
dipolar chromophores with relatively high TPA ability.
Although various electron-withdrawing heterocyclic moieties
such as triazole,1d pyridine,2 pyridinium,5f oxadiazoles,5a,b
benzothiazole6a and benzothiadiazole6b have been used in the
design of TPA active compounds, more extended heterocyclic
moieties such as phenanthrolines have been investigated only
recently by Prasad et al.7 These authors showed that 1,10-
phenanthrolines-containing p-conjugated chromophores with
electron donor substituents such as a dihexylamino group are
characterized by particularly large TPA cross-section values.
In addition, when these chromophores coordinate with a metal
center such as the nickel(II) ion, the resulting complexes do
not lose their excellent TPA ability, the nickel(II) chelated
complexes displaying red-shifted TPA bands compared with
their metal-ion free chromophores.7 This study, which can
be considered a springboard to the design of coordination
2,29:69,20-terpyridine] [X = NBu2 (TD1), N(C16H33)2 (TD2),
trans-CHLCH(C6H4)-p-N(C16H33)2 (TD3), CH3 (TD4), NO2
(TA); see Fig. 1] were prepared along with related novel
cationic Zn(II) complexes [TD3-Zn-TD3][PF6]2 (Zn1), [TD3-Zn-
TD4][PF6]2 (Zn2) and [TD3-Zn-TA][PF6]2 (Zn3) (see
Experimental).
Their photophysical and TPA characteristics are shown in
Table 1 whereas typical absorption and fluorescence emission
spectra are shown in Fig. 2.
The TPA induced photoluminescence (TPA-PL) method
requires luminescent compounds with a reasonable photo-
luminescence quantum efficiency (WF), generally larger than
0.10, in order to obtain reliable TPA cross-section values. By
choosing THF as solvent, WF values in the range 0.33–0.66
were obtained for terpyridines TD1, TD2, and TD3 whereas that
for complex [TD3-Zn-TD3][PF6]2 was 0.06 only. However, the
use of acetone or DMF as solvent afforded adequate WF
values (0.44–0.50) for the various Zn(II) complexes. All these
compounds exhibit large Stokes shifts, indicating that signifi-
cant nuclear reorganization takes place after excitation prior
to emission.1d The TPA-cross sections values are evidenced in
Table 1 and Fig. 3. The TPA response of terpyridines TD4 and
aDipartimento di Chimica Inorganica, Metallorganica e Analitica
dell’Universita` di Milano, Centro di Eccellenza CIMAINA, and Unita` di
Ricerca dell’INSTM di Milano, Via Venezian 21, 20133 Milano, Italy.
E-mail: dominique.roberto@unimi.it; Fax: +39 02 50314405;
Tel: +39 02 50314399
bIstituto di Scienze e Tecnologie Molecolari del CNR (ISTM), Via C.
Golgi 19, 20133 Milano, Italy
cInstitute for Polymers and Organic Solids, University of California
Santa Barbara, USA
TA could not be determined because their lmax, absorption is too
low (280 nm).
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Fig. 2 (a) Normalized absorption and fluorescence emission spectra
of free terpyridines. (b) Normalized absorption and fluorescence
emission spectra of Zn(II) complexes.
Fig. 1 Terpyridines investigated.
The TPA cross-section values for free ligands are remark-
ably high for simple dipolar molecules (87, 76 and 105 GM for
TD1, TD2, and TD3 respectively, at 720 or 815 nm) when
compared to that of AF-50 (d = 22 GM at 796 nm),1e which
has one of the largest d values so far observed for a D–p–A
structure and is usually referred as a TPA benchmark for
800 nm measurements.1d,5f The d values are similar for TD1 and
TD2 which differ only by the length of the alkyl chains on the
donor amino substituent whereas the d value of the more
p-delocalized terpyridine TD3 is higher and the TPA band red-
shifted with respect to TD1 and TD2 (Fig. 3). Such a trend is
expected since it is commonly known that the increase of the
conjugation length leads to an increase of the TPA activity.3b,5f
Coordination to a cationic Zn(II) center leads to a decrease of
Fig. 3 Two-photon absorption for free terpyridines and Zn(II)
complexes.
the TPA response, the homoleptic complex [TD3-Zn-TD3][PF6]2
(Zn1) showing a d value of 95 GM (at 815 nm) which
corresponds to about half that of two TD3 molecules.
The heteroleptic complexes [TD3-Zn-TD4][PF6]2 (Zn2) and
Table 1 Photophysical and TPA characteristics for various terpridines and related zinc complexes
Stokes shift/cm21b
TPA l(2)max/nm
TPA cross-section d /GMc
a
Compound
Absorption lmax/nm
Emission lmax/nm
WF
TD1
TD2
TD3
Zn1
Zn2
Zn3
a
358d
356d
399d
459e
453e
426g
453d
452d
516d
576e,f
577e
576g
0.39
0.33
0.66
0.44
0.46
0.50
5900
6000
5700
4400
4700
6100
720
720
815
815
815
830
87
76
105
95
77
30
b
Fluorescence quantum yield, determined at room temperature with fluorescein (WF = 0.92 in H2O) as a reference. Stokes shift: 1/labs21/lem
.
1 GM (Goppert2Mayer) = 1 6 10250 cm4 s photon21 molecule21
.
In THF. In acetone. f In THF, lmax, absorption and lmax, emission = 331 and
c
d
e
528 nm, respectively, and WF = 0.06. g In DMF; in acetone, lmax, absorption and lmax, emission = 462 and 558 nm, respectively, and WF = 0.01.
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[TD3-Zn-TA][PF6]2 (Zn3) have even lower values (77 GM at
815 nm and 30 GM at 830 nm, respectively). We note a
considerably smaller d value of [TD3-Zn-TA][PF6]2 with respect
to that of [TD3-Zn-TD3][PF6]2 suggesting that, like for organic
compounds, dipolar coordination complexes are less TPA
active than multipolar ones. A decrease (of ca. 20%) in the
TPA cross-section value was previously reported upon
coordination to Ni(II) of two phenantrolines bearing a strong
electron-donating group such as a dialkylamino group whereas
an enhance TPA response was observed upon coordination
to Ni(II) of phenanthrolines with weaker electron donors
such as alkyloxy and alkylthio groups.
a very strong TPA response.1f In the case of two-photon
excited fluorescence microscopy, high-performance fluoro-
phores must exhibit both high fluorescence quantum yields
(W) and large TPA cross-sections in the red–NIR range (700–
1200 nm), corresponding to the biological optimal window for
reduced photodamage.4c These requirements are fulfilled by
the family of terpyridines investigated. Besides, it appeared
that coordination to a Zn(II) metal center of these terpyridines
leads to some decrease of the TPA response, an observation
that can be explained by the 2F2S model.9
4. Experimental
Clearly, the effect of coordination to a metal center on the
TPA cross section of push–pull dipolar p-delocalized nitrogen
donor ligands deserves more investigations. However, it is
interesting to point out that the efficiency of push–pull dipolar
(D–p–A) systems has been described by a very simple two-
form two-state (2F2S) model developed by Barzoukas and
Blanchard-Desce.9 In this 2F2S model the electronic properties
of the push–pull molecular system are described starting from
two limiting electronic states: a neutral (D–p–A ) and a charge
transfer (D+–p–A2) one. The real electronic states of the
molecule are a mixture of the two limiting forms, and the
degree of mixing is specified by an empirical parameter MIX.
The TPA cross section is a symmetric function of the MIX
parameter, and shows a maximum efficiency for MIX values
approximately half-way between those of the neutral or charge
transfer form and the ‘‘cyanine’’ (i.e., 50% weight for the
neutral and charge transfer form) limit.9 The above 2F2S
model could explain the behaviour observed in the TPA
spectra of the coordination compounds investigated here.
Since coordination to a Zn(II) center leads to increased
acceptor properties of the terpyridine rings of push–pull
Hexadecylbromide, K2CO3, KI, POCl3, tBuOK, NH4PF6,
CH3OH, EtOH, CH2Cl2, anhydrous dimethylacetamide
and DMF (on molecular sieves), Zn(CH3CO2)2?2H2O and
terpyridine TD4 were purchased from Sigma-Aldrich and used
without further purification. Terpyridines TD1 and TA were
synthesized as already reported10 while TD2 and TD3 were
prepared as reported in Scheme 1 under nitrogen atmosphere,
using flasks that were previously dried over flame and cooled
under nitrogen flow. The novel zinc terpyridine complexes
were prepared as reported below, following a procedure
reported for similar complexes.11
Products were characterized by 1H-NMR (Bruker DRX-300
and 400 spectrometers) and UV–visible (Jasco V-530 spectro-
photometer) spectroscopy, in some cases mass spectrometry
(Varian VG9090 spectrometer) and elemental analysis which
dipolar ligands such as TD1 and TD2,
10e it reasonably modifies
the weight of the neutral and charge transfer form affecting the
ground electronic state, moving towards the ‘‘cyanine’’
structure, in agreement with the observed decrease of the
TPA cross section. When the complex of Zn(II) with two
terpyridine ligands is formed, if we consider that the electronic
state of Zn(II) does not mix with the one of the ligands, the
interaction between the ligands will be just a through space
interaction. Because of the geometrical form of the coordina-
tion compounds, the two ligands are quite far apart and
their interactions will be extremely weak. So it is likely that
cooperative interactions will be negligible. Therefore the
coordination compounds with two terpyridine ligands will
have a TPA cross section which is the sum of the TPA cross
section of the two single ligands but bound to the Zn(II) cation,
characterized both by a lower TPA cross section than the one
of the pure ligand.
3. Conclusion
In conclusion, this study provides evidence of the remarkably
high TPA activity of dipolar terpyridines bearing a donor
substituent, which appear as very attractive building blocks for
the design of TPA chromophores with practical applications.
For example, combining dipolar branches of terpyridines
within a three-branched octupolar structure is expected to give
Scheme 1 Synthesis of TD2 and TD3. (i) C16H33Br, K2CO3, KI, DMA;
t
(ii) POCl3, DMF. (iii) BuOK, THF; (iv) THF–EtOH, AcONH4. (v)
tBuOK, DMF.
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Fig. 4 Numbering for 1H NMR spectra.
were carried out at the Dipartimento di Chimica Inorganica,
1H-NMR (300 MHz, CDCl3, 25 uC, TMS): d (ppm) 7.19
Metallorganica ed Analitica of the Universita` di Milano.
1
For the numbering used in the attribution of the H-NMR
(dd, 2H, J = 7.0 Hz, J = 7.2 Hz, H3, H39), 6.61 (m, 3H, H2, H29,
H4), 3.23 (t, 4H, J = 7.4 Hz, N–CH2), 1.56 (m, 4H, N–CH2–
CH2–CH2–), 1.28 (m, 52H, –CH2), 0.87 (t, 6H, J = 6.8 Hz,
CH3). MS-FAB+ m/e 542 (M+H)+ (calcd for C38H71N m/e
541). Anal. Calcd. (found): C, 84.21 (84.29); H, 13.20 (13.11);
N, 2.59 (2.60).
signals, see Fig. 4.
Two-photon absorption (TPA) spectra of the compounds
studied were measured using TPA photoluminescence (TPA
PL) spectroscopy.8 Luminescence was excited via TPA by
directing tightly collimated (y120 mm in diameter), high-
intensity laser beam on a sample placed in a square spectro-
scopic cell. The emission was collected at 90u angle by a
high numerical aperture lens and directed to a spectrometer’s
entrance slit through IR-blocking filters. The radiation
dispersed by the spectrometer was detected by a thermo-
electrically cooled CCD camera (Roper Scientific PIXIS
10:400). Excitation pulses with typical duration of 90 fs and
maximum energy of approximately 6 nJ were produced by the
mode-locked Ti:sapphire laser (Spectraphysics Tsunami) with
repetition rate of 80 MHz. The laser’s wavelength was tuned
continuously within the spectral range 690–1000 nm. Neutral
density filter wheel was used to attenuate the energy of the
laser pulses down to desirable level.
4-(N,N-dihexadecylamino)benzaldehyde (2). Phosphoryl
chloride (0.9 mL, 9.65 mmol) was added dropwise to
anhydrous DMF (90 mL, 1.17 mol) at 0 uC under nitrogen
flow. The mixture was stirred at 0 uC for 70 min, then at room
temperature for 1 h. To the resulting yellow solution, heated at
95 uC, a solution of 1 (5.23 g, 9.65 mmol) in anhydrous DMF
(50 mL) was added. The reaction mixture was stirred at 95 uC
for 3 h. Removal of the solvent in vacuo afforded a thick
residue, which was taken up with CH2Cl2 (50 mL) and washed
several times with an aqueous satured solution of NaHCO3,
until pH was between 7 and 8. The organic layer was dried
over MgSO4 and evaporated. The brown solid thus obtained
was purified by column chromatography on silica (hexane :
Et2O = 9 : 1), affording 3.14 g (57%) of 2 as a white waxy solid.
1H-NMR (300 MHz, CDCl3, 25 uC, TMS): d (ppm) 9.70 (s,
1H, CHO), 7.70 (d, 2H, J = 8.8 Hz, H3, H39), 6.66 (d, 2H, J =
8.8 Hz, H2, H29), 3.32 (t, 4H, J = 7.3 Hz, N–CH2), 1.61 (m, 4H,
N–CH2–CH2–CH2–), 1.30 (m, 52H, –CH2), 0.87 (t, 6H, J =
6.6 Hz, CH3). MS-EI m/e 569 (calcd for C39H71NO m/e 569).
Anal. Calcd. (found): C, 82.18 (82.63); H, 12.55 (12.98); N,
2.45 (2.46).
TPA PL technique requires the use of a reference sample
with known TPA cross-section spectrum and fluorescence
quantum yield. In our experiments, we utilized 1025
M
aqueous solution of fluorescein (pH = 11). TPA cross-section
spectra of fluorescein were taken from the literature,12 and its
fluorescence quantum yield was measured using an integrating
sphere (WF = 0.92). Technical grade fluorescein was purchased
from Acros Organics and used without purification.
Synthesis of terpyridines
49-[4-(N,N-dihexadecylamino)phenyl]-2,29:69,20-terpyridine
(TD2). 2-Acetylpyridine (0.43 mL, 3.86 mmol) was slowly
added dropwise under nitrogen flow at room temperature to a
suspension of tBuOK (0.668 g, 5.95 mmol) in anhydrous THF
(20 mL) and the mixture was stirred at room temperature for
2 h. A solution of 2 (1.00 g, 1.75 mmol) in anhydrous THF
(6 mL) was thus added. After stirring overnight, 95% aq.
EtOH (30 mL) and solid AcONH4 (4.7 g, 61.25 mmol) were
added and the mixture refluxed for 4 h. The solvent was
removed in vacuo and 10% aq. HCl (10 mL) was added,
affording a red powder, which was filtered, dissolved in
CH2Cl2 (50 mL) and washed with 10% aq NaOH, until pH
was alkaline. The organic phase was dried over Na2SO4
and evaporated. The brown thick residue thus obtained
was stirred with CH3OH (10 mL), affording a yellow powder,
which was purified by column chromatography on silica
The preparation of TD2 and TD3 required N,N-dihexadecyl-
phenylamine (1) and 4-(N,N-dihexadecylamino)benzaldehyde
(2) as reagents (Scheme 1) which preparation is reported
below.
N,N-dihexadecylphenylamine(1).Hexadecylbromide(15.2mL,
50 mmol), K2CO3 (15.4 g, 110 mmol) and KI (1.32 g, 8 mmol)
were added to a solution of aniline (1.96 mL, 22 mmol) in
dimethylacetamide (80 mL) and the reaction mixture was
stirred at 160 uC for 16 h. Removal of the solvent under
vacuum afforded a thick residue, which was taken up with H2O
(100 mL) and extracted with CH2Cl2 (3 6 50 mL). The organic
phase was dried over Na2SO4, affording a light brown wax.
Purification by column chromatography on silica (hexane :
Et2O = 95 : 5) led to 9.1 g of 1 (76%) as a white solid.
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(CH2Cl2 : CH3OH : NH3 = 100 : 10 : 1), leading to 550 mg
(41%) of TD2 as a bright yellow solid.
J = 6.4 Hz, CH3). Anal. Calcd. (found): C, 69.58 (68.11); H,
8.23 (8.33); N, 5.32 (5.11).
1H-NMR (300 MHz, CDCl3, 25 uC, TMS): d (ppm) 8.73
(dd, 2H, J = 1.8 Hz, J = 5.0 Hz, H6, H60), 8.70 (s, 2H, H39,
H59), 8.66 (d, 2H, J = 7.9 Hz, H3, H30), 7.86 (m, 4H, H7,
H79, H4, H40), 7.33 (ddd, 2H, J = 1.2 Hz, J = 4.8 Hz, J =
6.0 Hz, H5, H50), 6.72 (d, 2H, J = 9.0 Hz, H8, H89), 3.32 (t,
4H, J = 7.0 Hz, N–CH2), 1.62 (m, 4H, N–CH2–CH2–CH2–),
1.26 (m, 52H, –CH2), 0.87 (t, 6H, J = 6.2 Hz, CH3). Anal.
Calcd. (found): C, 82.33 (82.25); H, 10.43 (10.40); N, 7.24
(7.35).
[Zn(CH3CO2)2TD3]. Solid TD3 (90.2 mg, 0.103 mmol) was
added to a colorless solution of Zn(CH3CO2)2?2H2O (22.6 mg,
0.103 mmol) in EtOH (25 mL). The reaction mixture was
stirred at room temperature for 30 min, then refluxed for 1 h.
Removal of the solvent under vacuum afforded 85 mg (78%) of
the desired complex as an orange powder.
1H-NMR (400 MHz, CDCl3, 25 uC, TMS): d (ppm) 8.96
(d, 2H, J = 5.1 Hz, H6, H60), 8.15 (s, 2H, H39, H59), 7.98 (d, 2H,
J = 8.1 Hz, H3, H30), 7.71 (t, 2H, J = 7.5 Hz, H4, H40), 7.61
(d, 2H, J = 7.8 Hz, H8, H89), 7.44 (m, 4H, H13, H139, H5, H50),
7.33 (d, 2H, J = 7.5 Hz, H7, H79), 7.05 (d, 1H, Jtrans = 16.2 Hz,
H10 o H11), 6.79 (d, 1H, Jtrans = 16.2 Hz, H10 o H11), 6.67 (d,
2H, J = 8.1 Hz, H14, H149), 3.32 (t, 4H, J = 6.3 Hz, N–CH2),
1.70 (m, 4H, N–CH2–CH2–CH2–), 1.27 (m, 52H, –CH2), 0.88
(t, 6H, J = 6.9 Hz, CH3). Anal. Calcd. (found): C, 73.73
(72.96); H, 8.76 (8.61); N, 5.29 (5.23).
49-(4-{2-[4-(N,N-dihexadecylamino)phenyl]ethenyl}phenyl)-
2,29:69,20-terpyridine (TD3). Potassium tert-butoxide (0.169 g,
1.5 mmol) was added to a solution of 4-(2,29:69,20-terpyridin-
49)-benzyl triphenyl phosphonium bromide
3 (0.500 g,
0.752 mmol), prepared as previously reported,9e in anhydrous
DMF (18 mL). The dark red solution was stirred under
nitrogen at room temperature for 45 min, then heated at 90 uC
for 30 min, after which solid 2 (0.429 mg, 0.752 mmol) was
added and the reaction mixture was stirred under nitrogen at
90 uC for 16 h. Removal of the solvent in vacuo afforded a
thick residue which was taken up with CH2Cl2 (100 mL) and
washed with H2O (3 6 60 mL). The organic layer was dried
over Na2SO4 and evaporated, to give a brown oily residue.
This product was stirred with MeOH (10 mL) overnight, to
afford 0.481 g of TD3 (73%) as a yellow–orange solid.
[Zn(CH3CO2)2TD4]. A solution of TD4 (130 mg, 0.4 mmol)
in EtOH (10 mL) was added to a colorless solution of
Zn(CH3CO2)2?2H2O (87.8 mg, 0.4mmol) in EtOH (10 mL).
The pale yellow reaction mixture was refluxed for 1 h.
Removal of the solvent in vacuo afforded 167 mg (82%) of
the desired complex as a white powder.
1H-NMR (400 MHz, CDCl3, 25 uC, TMS): d (ppm) 9.06 (d,
2H, J = 4.9 Hz, H6, H60), 8.31 (s, 2H, H39, H59), 8.22 (d, 2H, J =
8.0 Hz, H3, H30), 7.99 (dt, 2H, J = 1.6 Hz, J = 7.5 Hz, H4, H40),
7.65 (d, 2H, J = 8.1 Hz, H7, H79), 7.61 (dd, 2H, J = 5.1 Hz, J =
7.6 Hz, H5, H50), 7.38 (d, 2H, J = 8.0 Hz, H8, H89), 2.48 (s, 3H,
CH3), 1.98 (s, 6H, CH3CO2). Anal. Calcd. (found): C, 61.62
(61.54); H, 4.57 (4.96); N, 8.29 (8.13).
1H-NMR (300 MHz, CDCl3, 25 uC, TMS): d (ppm) 8.78 (s,
2H, H39, H59), 8.76 (d, 2H, J = 4.5 Hz, H6, H60), 8.70 (d, 2H, J =
7.9 Hz, H3, H30), 7.90 (m, 4H, H7, H79, H4, H40), 7.62 (d, 2H,
J = 8.1 Hz, H8, H89), 7.43 (d, 2H, J = 8.3 Hz, H13, H139),
7.37 (t, 2H, J = 6.5 Hz, H5, H50), 7.15 (d, 1H, Jtrans = 16.2 Hz,
H10 o H11), 6.95 (d, 1H, Jtrans = 16.2 Hz, H10 o H11), 6.65 (d,
2H, J = 8.3 Hz, H14, H149), 3.32 (t, 4H, J = 7.0 Hz, N–CH2),
1.62 (m, 4H, N–CH2–CH2–CH2–), 1.28 (m, 52H, –CH2), 0.90
(t, 6H, J = 6.8 Hz, CH3). Anal. Calcd. (found): C, 83.63
(83.38); H, 9.90 (10.06); N, 6.90 (6.77).
[TD3-Zn-TA][PF6]2. Solid TA (39.1 mg, 0.11 mmol) was
added to a refluxing solution of [Zn(CH3CO2)2TD3] (116.7 mg,
0.11 mmol) in CH3OH (15 mL). The resulting red mixture
was refluxed for 45 min. After cooling at room temperature, a
solution of NH4PF6 (50 mg, 0.30 mmol) in CH3OH (5 mL)
was added, leading to the immediate precipitation of a red
solid. After 45 min of stirring at room temperature, it was
collected and washed with a small amount of cool CH3OH and
H2O. The red powder thus obtained was dissolved in CH2Cl2
(15 mL), filtering the insoluble excess of NH4PF6 and finally
affording 135 mg (77%) of the desired complex as a red solid.
1H-NMR (400 MHz, CD3COCD3, 25 uC, TMS): d (ppm)
9.53 (s, 2H, Hc9, He9), 9.41 (s, 2H, H39, H59), 9.13 (m, 4H, H3,
H30, Hc, Hc0), 8.59 (s, 4H, Hg, Hg9, Hh, Hh9), 8.34 (m, 6H, H4,
H40, Hd, Hd0, H8, H89), 8.24 (m, 4H, H6, H60, Hf, Hf0), 7.90
(d, 2H, J = 8.3 Hz, H7, H79), 7.57 (m, 4H, H5, H50, He, He0),
7.52 (d, 2H, J = 8.6 Hz, H13, H139), 7.41 (d, 1H, Jtrans = 16.3 Hz,
H10 o H11), 7.14 (d, 1H, Jtrans = 16.3 Hz, H10 o H11), 6.77 (d,
2H, J = 8.7 Hz, H14, H149), 3.42 (m, 4H, N–CH2), 1.67 (m, 4H,
N–CH2–CH2–), 1.29 (m, 52H, –CH2), 0.89 (t, 6H, J = 7.0 Hz,
CH3). Anal. Calcd. (found): C, 62.13 (62.26); H, 6.80 (6.49); N,
7.61 (7.40).
Synthesis of complexes
[TD3-Zn-TD3][PF6]2. Solid TD3 (322.3 mg, 0.368 mmol) was
added to a colorless solution of Zn(CH3CO2)2?2H2O (40.4 mg,
0.184 mmol) in CH3OH (19 mL). The reaction mixture was
stirred at room temperature for 30 min, then refluxed for
further 30 min. To the red solution thus obtained, cooled at
room temperature, a solution of NH4PF6 (66 mg, 0.405 mmol)
in CH3OH (5 mL) was added, leading to the immediate
precipitation of a red solid. After 45 min of stirring at room
temperature, it was collected and washed with a small amount
of cool CH3OH, leading to 287 mg (74%) of the desired
complex as a red powder.
1H-NMR (400 MHz, CDCl3, 25 uC, TMS): d (ppm) 8.73 (s,
2H, H39, H59), 8.55 (d, 2H, J = 8.1 Hz, H3, H30), 8.03 (d, 2H,
J = 7.9 Hz, H8, H89), 7.98 (t, 2H, J = 7.5 Hz, H4, H40), 7.76
(d, 2H, J = 4.5 Hz, H6, H60), 7.56 (d, 2H, J = 7.8 Hz, H7, H79),
7.35 (m, 4H, H13, H139, H5, H50), 7.04 (d, 1H, Jtrans = 15.9 Hz,
H10 o H11), 6.78 (d, 1H, Jtrans = 15.9 Hz, H10 o H11), 6.63 (d,
2H, J = 8.04 Hz, H14, H149), 3.29 (m, 4H, N–CH2), 1.61 (m,
4H, N–CH2–CH2–CH2–), 1.29 (m, 52H, –CH2), 0.90 (t, 6H,
[TD3-Zn-TD4][PF6]2. Procedure 1. A solution of TD4 (27.5 mg,
0.0852 mmol) in CH3OH (5 mL) was added to a refluxing
This journal is ß The Royal Society of Chemistry 2006
J. Mater. Chem., 2006, 16, 1439–1444 | 1443

View Article Online
O. Ruel, J. B. Baudin, D. Alcor, J. F. Allemand, A. Meglio and
L. Jullien, Angew. Chem., Int. Ed., 2004, 43, 4785.
2 B. A. Reinhardt, L. L. Brott, S. J. Clarson, A. G. Dillard,
J. C. Bhatt, R. Kannan, L. Yuan, G. S. He and P. N. Prasad,
Chem. Mater., 1998, 10, 1863.
solution of [Zn(CH3CO2)2TD3] (90.2 mg, 0.0852 mmol) in
CH3OH (12 mL). The resulting dark orange mixture was
refluxed for 15 min. After cooling at room temperature, a
solution of NH4PF6 (30 mg, 0.184 mmol) in CH3OH (3 mL)
was added, leading to the immediate precipitation of a dark
orange solid. After 45 min of stirring at room temperature, it
was collected and washed with a small amount of cool
CH3OH, affording 100 mg (75%) of the desired complex as
an orange solid.
3 See, for example: (a) L. Ventelon, L. Moreaux, J. Mertz and
M. Blanchard-Desce, Chem. Commun., 1999, 2055; (b) M. Rumi,
J. E. Ehrlich, A. A. Heikal, J. W. Perry, S. Barlow, Z.-Y. Hu,
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12, 284; (d) L. Ventelon, S. Charier, L. Moreaux, J. Mertz and
M. Blanchard-Desce, Angew. Chem., Int. Ed., 2001, 40, 2098; (e)
O. Mongin, L. Porre`s, L. Moreaux, J. Mertz and M. Blanchard-
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4 See, for example: (a) B. R. Cho, K. H. Son, H. L. Sang, Y.-S. Song,
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Procedure 2. Solid TD3 (135 mg, 0.152 mmol) was added to
a solution of [Zn(CH3CO2)2TD4] (78 mg, 0.152 mmol) in
CH3OH (28 mL). The resulting orange mixture was stirred at
room temperature for 30 min, then refluxed for 45 min. After
cooling at room temperature, a solution of NH4PF6 (60 mg,
0.368 mmol) in CH3OH (5 mL) was added, leading to the
immediate precipitation of a red solid. After 45 min of stirring
at room temperature, it was collected and washed with a small
amount of cool CH3OH and H2O, affording 180 mg (75%) of
the desired complex as a red solid.
1H-NMR (400 MHz, CD3COCD3, 25 uC, TMS): d (ppm)
9.41 (s, 2H, H39, H59), 9.38 (s, 2H, Hc9, He9), 9.12 (m, 4H, H3,
H30, Hc, Hc0), 8.27 (m, 12H, H4, H40, H6, H60, H8, H89, Hd, Hd0,
Hf, Hf0, Hg, Hg9), 7.89 (d, 2H, J = 8.1 Hz, H7, H79), 7.58 (m,
4H, H5, H50, He, He0), 7.52 (d, 2H, J = 8.6 Hz, H13, H139),
5 See, for example: (a) S.-J. Chung, K.-S. Kim, T.-C. Lin, G. S. He,
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C. W. Spangler, Opt. Lett., 2001, 26, 1081; (d) S.-J. Chung,
T.-C. Lin, K.-S. Kim, G. S. He, J. Swiatkiewicz, P. N. Prasad,
G. A. Baker and F. V. Bright, Chem. Mater., 2001, 13, 4071; (e)
J. Yoo, S. K. Yang, M.-Y. Jeong, H. C. Ahn, S.-J. Jeon and
B. R. Cho, Org. Lett., 2003, 5, 645; (f) A. Abbotto, L. Beverina,
R. Bozio, A. Facchetti, C. Ferrante, G. A. Pagani, D. Pedron and
R. Signorini, Chem. Commun., 2003, 2144; (g) O. Mongin,
J. Brunel, L. Porre`s and M. Banchard-Desce, Tetrahedron Lett.,
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A. Rebane, Z. Suo and C. W. Spangler, J. Phys. Chem. B, 2003,
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7.41 (d, 1H, Jtrans = 16.3 Hz, H10 o H11), 7.14 (d, 1H, Jtrans
=
16.2 Hz, H10 o H11), 6.77 (d, 2H, J = 8.6 Hz, H14, H149), 3.42
(m, 4H, N–CH2), 1.67 (m, 4H, N–CH2–CH2–), 1.29 (m, 52H,
–CH2), 0.89 (t, 6H, J = 7.0 Hz, CH3). Anal. Calcd. (found): C,
64.15 (64.05); H, 6.68 (6.77); N, 6.31 (6.13).
Acknowledgements
We thank deeply Prof. Camilla Ferrante (Universita` di
Padova) for fruitful discussions and Dr Alexander
Mikhailovsky for help with TPA induced photoluminescence
measurements. This work was supported by the Ministero
dell’Istruzione, dell’Universita` e della Ricerca (Programma di
ricerca FIRB 2001, Research Title: Nano-organization of
hybrid organo-inorganic molecules with magnetic and non
linear optical properties; Programma di ricerca FIRB 2003,
Research Title: Molecular compounds and hybrid nano-
structured materials with resonant and non resonant optical
properties for photonic devices).
7 Q. Zheng, G. S. He and P. N. Prasad, J. Mater. Chem., 2005, 15,
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8 S. J. K. Pond, O. Tsutsumi, M. Rumi, O. Kwon, E. Zojer,
J.-L. Bre´das, S. R. Marder and J. W. Perry, J. Am. Chem. Soc.,
2004, 126, 9291.
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